From our experience, we feel that a tremendous quantity of bone chips, as is used in cases of spondylolisthesis, can be placed over the dura with impunity, if the nerve roots are covered by muscle or fat. The method is simple and quick, and in most cases it results in solid fusion. It is somewhat difficult to obtain a solid fusion from the fourth lumbar vertebra to the sacrum without taking chips from an ilium.
Formerly, fusion was routinely carried out from the fourth lumbar vertebra to the sacrum, after removal of a ruptured nucleus of the fourth lumbar vertebra; now the fusion is extended only from the fourth to the fifth lumbar vertebra in these cases.
To date, the young woman previously mentioned is the only patient in whom there has been definite evidence of failure of fusion.
T h e conclusions which we have drawn from this work are that fusion of the adjacent segments should be performed following operation for disorders of the intervertebral disc, and that a chip fusion, as described, is a satisfactory operative procedure.